This is an article I've wanted to write for a while... so here it is on a long weekend. Any questions please free to ask.

Fiber-Reinforced Polymer (FRP) is a composite material which consists of fibers of high strength and/or high stiffness embedded in or bonded to a matrix material.

The fiber, as most of you know, are materials such as carbon fiber, Kevlar, and glass fiber. The primary purpose of the fiber is to carry load.

Fibers are literally like your hair. Therefore without a bonding agent the fibers would simply fall apart. That's why there is the matrix material which acts as the "glue" to hold the fibers in desired locations and directions. Common matrix materials can be epoxy, polyester, etc.

Myth #1: There is no such thing as 100% carbon fiber. As mentioned above, you must have a matrix material to hold the fibers together. Typically, aerospace-grade CF composites can have up to 60% fiber content (40% matrix), beyond which you could have bonding issues between the fibers. As I will discuss later, some times having all fibers as CF be not be the most desirable.

Myth #2: CF is not always the best material in every application. CF has been very popular these days on automobiles and aerospace applications because they offer very good properties at a light weight. (aka high strength/stiffness-to-weight ratio)

However, CF is generally brittle and cannot absorb a lot of energy (i.e. impact). And this is why the hull of a boat typically uses glass fiber because it needs to take in a lot of energy from the waves, be low cost, and weight is not as important.

Contrary to what many may think, S-glass (a type of glass fiber) is actually stronger than most forms carbon fibers. (not the case in terms of stiffness)

Sometimes the best structure may be a combination of various fiber layers (laminas) to get the best of all worlds (i.e. M3's roof). For example, on an airplane body you may want layers of CF for strength/stiffness, and have a layer of Kevler to prevent rupturing (think a bird hitting the plane at high speed). In some applications you would also add a honeycomb layer in between fiber layers to create a larger cross sectional area to increase the bending stiffness with minimal weight addition. Note that the honeycomb itself is not designed to take much of any loads at all.

Myth #3: Weaved fibers (common on aftermarket parts) are generally weaker than unidirectional fibers (non-weaved fibers in single directions). The main purpose of using a weaved fiber is for easier handling during manufacturing. In a weaved fabric the fibers twist and turn which creates stress concentrations and reduces the strength of fibers.

If there is interest I can write more about how composites are made as well as carbon-carbon/carbon-ceramic brakes.